The present invention relates generally to the heat treatment of metals and alloys, including aluminum alloy castings. More particularly, the invention relates to systems, methods, and articles of manufacture to predict the heat transfer coefficient in air and/or gas quenched castings after solution treatment.
The increasing demand of reducing weight and improving fuel efficiency has lead to the use of cast aluminum alloys in critical automotive components such as engine blocks, cylinder heads, and suspension parts. To improve mechanical properties, the aluminum castings are usually subject to a full T6/T7 heat treatment, which includes a solution treatment at a relatively high temperature, quench in a cold medium such as water or forced air, then age hardening at an intermediate temperature. A significant amount of residual stresses can be developed in aluminum castings during the quenching process. The existence of residual stresses, in particular tensile residual stresses, can have a significant detrimental influence on the performance of a structural component. In many cases, the high tensile residual stresses can result in a severe distortion of the component, and they can even cause cracking during quenching or subsequent manufacturing processes.
The amount of residual stresses produced in cast aluminum components during quenching depends on the quenching rate and the extent of non-uniformity of the temperature distribution in the entire casting. A rapid quenching, such as water quenching, can produce a significant amount of tensile residual stresses, particularly in a complex aluminum component with different wall thicknesses. Consequently, air quenching has been used increasingly in the heat treatment of cast aluminum components. Compared to water quenching, air quenching can control the quenching rate more uniformly so that the residual stresses and distortion can be minimized.
Heat transfer of a hot metal work piece during air and/or gas quenching is dependent on the heat transfer coefficient (HTC) at the interface between the hot metal object and the quenching air and/or gases. The use of accurate HTC boundary conditions during the computational simulation is needed for reliable prediction of the material behavior during quenching. However, experimental determination of the HTC boundary condition during quenching is not only costly, but also difficult, particularly for a work piece with a complex geometry. As a result, a uniform and constant HTC boundary condition is often assumed in the quenching simulation. This can result in a significant error between the simulation and the actual measurements.
Therefore, there is a need for a method of predicting the distribution of heat transfer coefficients of the entire heat transfer interfaces between the hot metal object and the quenching media.